Device and process for stimulation and cleaning of a liquid-filled well

ABSTRACT

The invention relates to a device for cleaning a liquid-filled well ( 10 ) comprising a tubular vessel ( 21 ), the interior of which contains at least one combustion chamber ( 30 ) and at least one hollow chamber ( 25 ) arranged in longitudinal succession, the combustion chamber ( 30 ) being at least partly filled with a fuel ( 31 ) and having an igniter ( 32 ), and the vessel ( 21 ) having at least one inflow orifice through which well fluid can flow from the outside into the vessel ( 21 ), wherein the at least one inflow orifice is provided with a closure device ( 42 ) comprising at least one closure element which loses its integrity on exceedance of a given temperature, such that the closure device ( 42 ) opens. The invention further relates to a process for stimulating and cleaning a liquid-filled well using an inventive device.

The present invention relates to a device for cleaning a liquid-filled well comprising a tubular vessel, the interior of which contains at least one combustion chamber and at least one hollow chamber arranged in longitudinal succession, the combustion chamber being at least partly filled with a fuel and having an igniter, and the vessel having at least one inflow orifice through which well fluid can flow from the outside into the vessel. The invention further relates to a process for stimulating and cleaning a liquid-filled well using the inventive device.

In the production of fluids such as mineral oil or natural gas from underground rock strata, the productivity of a production system depends to a high degree on the permeability of the rock strata which adjoin the well. The more permeable these rock strata, the more economically a deposit can be operated. Both in the development and during the production from a deposit, there may be a reduction in permeability and hence adverse effects.

In the production of wells, both for production and for injection wells, there may be slurrying of the porous rock strata during the drilling and cementing operation, such that the permeability falls. Moreover, there is a change in the stress, pressure and deformation state of the rock in the course of drilling, the result of which is that zones of elevated density and low permeability form in a circle around the well. During the operating phase of the well, paraffins, asphaltenes and high-viscosity tars are frequently deposited in the rock, these reducing the productivity of the well.

The best-known methods for counteracting a reduction in the permeability of the well region include various perforation technologies, vibration and heat treatment, the use of chemically active substances and swabbing. In one kind of perforation technology, gas generators which are operated with solid fuels are used. They are designed as encased or unencased explosive charges and, after ignition, generate hot gases which result in a pressure rise in the well and the adjacent rock strata. Typically, gas generators are used in the well at the level of the production zone in order to cause new perforations in the rock or widen existing perforations owing to the pressure rise.

Russian patent specification RU 2311529 C2 discloses a process for well stimulation by means of a gas generator in oil and gas production. The device includes tubular cylindrical explosive charges, ignition charges and a geophysical cable, called a logging cable, with securing elements for the explosive charges. The burnoff of the cylindrical explosive charges in the well results in thermal gas treatment and compressed air treatment of the rock. If a perforation has been conducted beforehand, the perforation channels are widened and cleaned, and cracks form in the rock.

The document RU 2178065 C1 discloses a further gas generator which is used in liquid-filled wells. The gas generator comprises fuel charges which, when they burn off, generate hot gas which escapes into the well fluid surrounding the gas generator. The liquid is heated and begins to boil. On completion of the thermal gas treatment, valves in the gas generator are opened, such that liquid can flow rapidly into the hollow interior thereof. This causes a rapid pressure drop in the already boiling liquid, resulting in explosive vaporization of the liquid. This generates new orifices in the rock and widens existing orifices.

The document RU 2211313 C1 likewise describes a hollow gas generator which is intended, after a thermal gas treatment of the well fluid surrounding it, to accommodate the latter in the hollow interior thereof. The interior of this gas generator is divided into several chambers by membranes. The well fluid first flows into a first chamber. The pressure which builds up destroys the membrane, and the liquid flows into the next chamber. This causes a sequence of pressure pulses which lead to the formation of new and widened cracks and orifices in the rock.

Even though several approaches to well stimulation are already known, there is still a need for improvement and enhanced efficiency in the production of mineral oil or natural gas from underground deposits.

It was an object of the present invention to provide a device and a process for well stimulation, by means of which the permeability of the rock can be improved in a targeted and efficient manner around a region of the well. The device should be producible in a simple manner in terms of construction and inexpensively.

This object is achieved by the subject matter of the invention as described in claim 1. Further advantageous embodiments of the invention can be found in the dependent claims. A further part of the subject matter of the invention is specified in process claim 11 and the claims dependent thereon.

The inventive device for cleaning a liquid-filled well comprises a tubular vessel, the interior of which contains at least one combustion chamber and at least one hollow chamber arranged in longitudinal succession, the combustion chamber being at least partly filled with a fuel and having an igniter. The vessel has at least one inflow orifice through which well fluid can flow from the outside into the vessel. The at least one inflow orifice is provided with a closure device comprising a closure element which loses its integrity on exceedance of a given temperature, such that the closure device opens.

The process according to the invention for stimulation and cleaning of a liquid-filled well comprises the following steps:

-   -   (a) introducing an inventive device into the well,     -   (b) igniting the fuel in the at least one combustion chamber,     -   (c) thermally opening the closure element of the at least one         inflow orifice, such that well fluid can flow into the at least         one hollow chamber,     -   (d) depending on the specific configuration of the device,         optionally closing the at least one inflow orifice, and     -   (e) withdrawing the device from the well.

The vessel is preferably secured to a geophysical cable, which is also referred to as a “logging cable”. With the aid of this, the vessel can be lowered from the surface of the well into the well by known means such as a hoist, and be removed again therefrom.

In a preferred embodiment of the process according to the invention, in step (a), the device is positioned in the well such that the combustion chamber is at the level of the perforation region of the production zone. The perforation region is understood here and hereinafter to mean the region of a production zone in which perforation holes and perforation channels are already present. Frequently, the axial extent of the perforation region corresponds to the thickness of the rock stratum from which the fluid, for example mineral oil or natural gas, is to be produced.

It is additionally preferable when, step (c) is preceded by positioning of the device in the well such that the at least one inflow orifice is at the level of the perforation region of the production zone.

In a further advantageous embodiment of the process according to the invention, step (c) is not initiated until the temperature of the outer wall of the inventive device in the region of the at least one combustion chamber has cooled to the boiling temperature of the well fluid in this region. The time interval between the ignition of the fuel in the combustion chamber and the cooling of the outer wall below the boiling temperature of the well fluid can already be estimated prior to the use of the device. An exact temperature determination is not required.

The tubular vessel may have a one-piece or a multipart design. The outer wall thereof is manufactured from a material which withstands the pressure and temperature stresses during the burnoff of the fuel. The choice of the material and configuration parameters, such as the wall thickness, depend on factors including the conditions in the well provided for the use, and on the properties and the amount of the fuel used.

Firstly, the vessel should be stable under the use conditions required; secondly, very good heat transfer is desired from the interior of the vessel to the outer wall thereof, in order to be able to utilize the energy generated by the burnoff of the fuel in a very efficient manner.

In a preferred configuration of the invention, the outer wall of the vessel is manufactured from a steel, especially from a high-strength, ductile steel. The inventive vessels used are more preferably pipes as typically used for production of oil or gas. Such pipes are usually manufactured from steel with an internal diameter of 8 to 40 cm and a length of 1 to 15 m. The wall thickness thereof is typically 1 to 10 mm. The diameter is advantageously selected such that it is 10% to 30% less than the internal diameter of the well in the region in which the device is used.

The vessel preferably has a circular cross section. However, the invention also covers other cross-sectional shapes, in which case the external diameter is understood to mean the greatest distance between two points on the cross-sectional area.

In the interior of the vessel, there is at least one combustion chamber at least partly filled with a fuel. The fuel may be present in the combustion chamber in different forms, for example as a solid body, pasty mass or finely divided bulk material. The solid body may have been produced, for example, by pressing with or without binder.

In preferred configurations of the invention, the fuel used is a metallothermic mixture. “Metallothermic mixtures” refer here and hereinafter to mixtures of metals with metal oxides which, after activation of the redox reaction, are converted exothermically to form the metal originally present in the metal oxide. According to the fuel used, the burnoff in the interior of the combustion chamber can give rise to temperatures well above 1000° C. Particularly preferred fuels are a subgroup of the metallothermic mixtures in which aluminum is used as a reaction partner of the metal oxides. Such mixtures are referred to hereinafter as “aluminothermic”. Especially preferred are mixtures comprising aluminum as a reducing agent and CuO, FeO, Fe₂O₃, Fe₃O₄, TiO₂, Cr₂O₃ and/or SiO₂ as an oxidizing agent. Such aluminothermic mixtures are inexpensive compared to other metallothermic mixtures and cover a wide use range with respect to the ignition temperature, the maximum temperature which evolves in the course of burnoff of the fuel, and the burnoff rate.

“Thermite” refers hereinafter to a mixture of iron(III) oxide and aluminum which is produced by and can be purchased from, for example, Elektro-Thermit GmbH & Co. KG (Halle/Saale). The temperature range which arises as the thermite reaction proceeds and the reaction enthalpy which is released can be adjusted by appropriate selection of the reaction partners and optionally the addition of additives. Patent specification RU 2291289 C2 discloses, as well as the abovementioned thermite mixtures, further metallothermic mixtures such as nickel(II) oxide and magnesium, iron(III) oxide and silicon, chromium(III) oxide and magnesium, molybdenum(VI) oxide and silicon and aluminum, vanadium(V) oxide and silicon. The burnoff of these mixtures can give rise to temperatures up to 2500° C. A further class of metallothermic mixtures including iron oxide, aluminum powder, alumina and a metal phosphate binder is known from document RU 2062194 C1. These mixtures have a comparatively low specific exothermicity and a maximum temperature in the course of burnoff of about 1930° C.

In the combustion chamber, there is additionally at least one igniter for ignition of the fuel. The choice of igniter depends on the fuel used. For example, it is possible to use electrical igniters such as electrical light arc igniters or spiral igniters, or chemical igniters, provided that they have sufficient activation energy. Suitable chemical igniters are, for example, mixtures ignitable at temperatures below the ignition temperature of the fuel. Examples of suitable igniters are mixtures of (proportions by mass in percent in brackets):

-   -   SiO₂ Mg (55/45),     -   MnO₂/Al dust/Al dust/Mg (68/7.5/7.5/17),     -   BaO₂/Mg (88/12).

These mixtures are ignited with the aid of electrical pulses, for example by the abovementioned electrical igniters. The electrical igniters are preferably activated by means of a conductive cable which is conducted from the surface of the well to the electrical igniter along the logging cable or integrated within the logging cable.

The longitudinal dimension of the combustion chamber is more preferably selected such that it corresponds to the axial dimension of the well through the perforation region.

In addition, within the vessel, there is at least one hollow chamber suitable for accommodating well fluid. The combustion chamber and hollow chamber are arranged in longitudinal succession, “longitudinal” being understood to mean the direction of the axis of the tubular vessel. Terms used hereinafter such as “top”, “above”, “bottom”, “below” relate to the alignment of the vessel in typical vertical wells. The hollow chamber and combustion chamber may directly adjoin one another, with or without a separating element between them. It is also possible for further chambers to be provided between the combustion chamber and the hollow chamber. The examples are used to illustrate preferred embodiments in detail below.

According to the invention, the tubular vessel has at least one inflow orifice through which well fluid can flow into the vessel from the outside. The inflow orifice is provided with a closure device which in turn comprises at least one closure element. In terms of its construction and material selection, the closure element is designed such that it loses its integrity on exceedance of a given temperature, such that the closure device opens.

In a preferred configuration of the invention, the closure device comprises, as well as the closure element, a further component which closes the inflow orifice, more particularly a plug present in the inflow orifice. The closure element connects the inflow orifice to the further component. As soon as the closure element is exposed to a temperature exceeding a given limit, the closure element loses its integrity, and the further component can move out of the inflow orifice under the pressure of the adjacent well fluid, such that the liquid passes into the vessel. In this configuration, the closure element is preferably a weld seam or an adhesive bond.

In a further preferred configuration of the invention, the closure device consists merely of the closure element, preferably in the form of a plug which closes the inflow orifice, loses its integrity on exceedance of a given temperature limit and as a result opens the inflow orifice. Such a closure element is advantageously manufactured from a plastic or a metal, and the material is selected such that its melting point corresponds to the given temperature limit. Suitable materials are, for example, plastics having a melting temperature within the range from 150° C. to 500° C. or aluminum alloys having melting temperatures within the range from 600° C. to 800° C.

In embodiments of the invention in which several inflow orifices are present, each is provided with a closure device. The closure devices may also have a coherent design, for example in the form of a lining of the inner wall of the vessel which extends over several inflow orifices and is manufactured from a material which, on exceedance of the given temperature limit, loses its integrity. The number of inflow orifices is preferably from 1 to 10. The total cross-sectional area of all inflow orifices together is preferably at least as great as the cross-sectional area of the interior of the hollow chamber.

In some embodiments of the inventive device, separating elements are used to separate adjacent chambers from one another. The separating elements preferably extend over the entire inner cross section of the vessel and run essentially at right angles to the longitudinal axis of the vessel. Particularly preferred separating elements are disk-shaped or cylindrical structures made of plastic or metal, the external diameter of which is slightly greater than the internal diameter of the vessel. A combustion chamber in this case can be produced, for example, by first introducing fuel into the vessel and then pressing a separating element into the vessel, such that the combustion chamber is closed.

In one configuration of the invention, the entire separating element is manufactured from a material which, on exceedance of a given temperature, loses its integrity. The effect of the thermal evolution in the course of burnoff of the fuel in this case is that the entire separating element loses its integrity. In a further configuration, only the means by which the separating element is secured in the tubular vessel are manufactured from such a material. In this case, in the course of burnoff of the fuel, only the securing of the separating element loses its integrity, such that the separating element is freely mobile within the vessel. Materials suitable for production of the separating elements or of the securing means thereof for this embodiment are, for example, plastics having a melting temperature within the range from 150° C. to 500° C. or aluminum alloys having melting temperatures in the range from 600° C. to 800° C.

In a preferred configuration of the inventive device, the vessel is configured as a one-piece pipe in which the chambers are separated from one another by separating elements extending over the entire pipe cross section within the pipe.

In a further preferred configuration of the inventive device, the vessel comprises two or more tubular vessels which form the chambers or parts of the chambers and the ends of which are connected via connecting elements. The vessels may be connected via connecting elements in different ways at the ends thereof. A manner which is simple to implement involves screwing the vessels together by means of the connecting elements, for example by providing the vessels with an outer screw thread onto which a tubular connecting element with an inner screw thread is screwed. A further means of connection results from provision of each of the ends of the vessels to be connected with a flange as a connecting element, and connection of the flanges to one another, for example by screw connection. It is also easily possible to use swivel nuts or a bayonet mount, for example, to establish connections between the tubular vessels.

To perform the process according to the invention for stimulation and cleaning of a liquid-filled well, an inventive device is first introduced into the well. The device is preferably positioned in the well such that the combustion chamber is at the level of the perforation region of the production zone. Subsequently, the fuel in the combustion chamber is ignited. Proceeding from the igniter, the fuel in the combustion chamber burns off, forming a reaction front which passes through the combustion chamber in the course of burnoff. In a preferred variant of the process according to the invention, the vessel is pulled upward or lowered downward continuously at a speed corresponding to the speed of the reaction front in the segment of the vessel in the process of burnoff. The evolution of heat strongly heats the well fluid surrounding the device in the region of the combustion chamber in the process of burnoff, preferably within temperature ranges of the boiling point thereof. The hot fluid and the vapor which forms clean the adjoining perforation region of the well.

As soon as the reaction front reaches the region of the combustion chamber where the closure element is present, the closure element loses its integrity due to the increase in temperature in the environment thereof. This thermal opening of the closure element opens the at least one inflow orifice of the vessel, and well fluid flows into the vessel, more particularly into the hollow chamber. Finally, the device is withdrawn from the well. The arrangement and configuration of the inflow orifices and optionally the closure elements thereof ensures that the well fluid accommodated within the vessel remains enclosed within the vessel while it is being withdrawn from the well.

In a preferred embodiment of the inventive device, the combustion chamber is at the lower end of the tubular vessel. The inflow orifice with its closure device is arranged at the lower end of the tubular vessel. The hollow chamber is arranged above the combustion chamber; it preferably reaches upward as far as the upper end of the vessel. In this configuration of the device, it is advantageous when the igniter is arranged within or at the fuel at the upper end of the combustion chamber. The igniter is more preferably present in the upper quarter of the fuel-filled volume of the combustion chamber. The hollow chamber may directly adjoin the combustion chamber. The hollow chamber is preferably separated by a separating element from the combustion chamber, said separating element being manufactured from a material which, when the fuel burns off, loses its integrity. In both cases, after the burnoff, in addition to the hollow chamber, the part of the combustion chamber not filled with burnoff residues is also available for accommodation of well fluid.

In a further preferred variant of this embodiment, the inflow orifice is configured so as to narrow from the inside outward, more preferably in the form of a cone. The closure device comprises a plug whose shape is matched to the inflow orifice and which is provided with a securing device which restricts the axial movement thereof away from the inflow orifice. The plug is connected in a thermally releasable manner to the inside of the end by virtue of a closure element, especially a weld seam or adhesive bond. The plug is manufactured from a material which withstands the temperatures that exist in the course of burnoff of the fuel. Only the closure element loses its integrity when the fuel is burnt off and releases the plug.

In a particularly preferred configuration, the securing device comprises a connecting element and a weight element which is outside the vessel. The connecting element is fixed to the weight element and the plug. The connecting element may be rigid or flexible and is manufactured from a material which withstands the temperatures which exist in the course of burnoff of the fuel. A rigid connecting element used is preferably a pole, and a flexible connecting element used is preferably a chain or a rope. The connecting element is preferably manufactured from a high-strength steel. The radial extent of the weight element at least in one spatial direction is greater than the diameter of the inflow orifice on the outside of the lower end of the vessel. This ensures that the weight element cannot get inside the vessel.

To perform the process according to the invention according to this configuration, the tubular vessel is first introduced into the well and preferably positioned such that the combustion chamber is at the level of the perforation region of the production zone. Subsequently, the fuel in the combustion chamber is ignited. Proceeding from the igniter, the fuel burns off within the combustion chamber, forming a reaction front which runs downward through the combustion chamber in the course of burnoff. If a separating element is present between the combustion chamber and the hollow chamber, it loses its integrity owing to the thermal evolution in the course of burnoff of the fuel. As soon as the reaction front reaches the lower region of the combustion chamber where the closure element is present, the latter loses its integrity owing to the temperature increase in the environment thereof. The plug becomes detached from the inflow orifice and opens it, such that well fluid can flow into the hollow chamber. On completion of the inflow operation, the vessel is withdrawn from the well in the upward direction. Under the action of gravity, the plug falls back into the inflow orifice under its own weight and closes it. This effect may be enhanced by the weight of the weight element, which pulls downward on the plug during the withdrawal of the vessel. The well fluid which has flowed into the vessel is enclosed therein and can be conveyed to the surface. This inventive configuration is particularly suitable for cleaning the well bottom.

In a further preferred embodiment of the inventive device, the combustion chamber is at the lower end of the tubular vessel. Above the combustion chamber is arranged the hollow chamber. Above the hollow chamber in turn is arranged an orifice chamber which is separated from the hollow chamber by a separating element. In the wall of the orifice chamber, there is at least one inflow orifice with its closure device. In the orifice chamber, a further igniter and further fuel are present, said fuel, when it burns off, generating a temperature at which both the at least one closure element and the separating element from the hollow chamber lose their integrity.

In this variant, the combustion chamber is more preferably filled completely with fuel, and the igniter is present in or at the fuel at the upper end of the combustion chamber. The hollow chamber may directly adjoin the combustion chamber. The hollow chamber is preferably separated from the combustion chamber by a separating element manufactured from a material which, when the fuel burns off, loses its integrity. In both cases, after the burnoff, in addition to the hollow chamber, the part of the combustion chamber not fulfilled by burnoff residues is available for accommodation of well fluid. More preferably, the orifice chamber is at the upper end of the tubular vessel and the at least one inflow orifice is provided at the upper end of the orifice chamber. Most preferably, several inflow orifices are provided.

To perform the process according to the invention, the inventive device is first introduced into the well and preferably positioned such that the combustion chamber is at the level of the perforation region of the production zone. Subsequently, the fuel in the combustion chamber is ignited. Proceeding from the igniter, the fuel burns off in the combustion chamber, forming a reaction front which passes downward through the combustion chamber in the course of burnoff. If a separating element is present between the combustion chamber and the hollow chamber, it loses its integrity owing to the thermal evolution in the course of burnoff of the fuel. On completion of the burnoff in the combustion chamber, the further fuel is ignited with the aid of the further igniter in the orifice chamber. The burnoff generates a temperature at which both the closure elements and the separating element from the hollow chamber lose their integrity. The inflow orifices are opened as a result, and well fluid flows into the interior of the vessel. In this embodiment, the closure of the inflow orifices after the inflow of the well fluid is not required, since the inflow orifices are at the upper end of the vessel. The well fluid is enclosed within the vessel and can be withdrawn from the well in the upward direction with the vessel.

In preferred configurations, the igniters of the combustion chamber and of the orifice chamber are ignitable independently of one another. This enables offset phases of well stimulation by burnoff of the fuel in the combustion chamber on the one hand and of cleaning of the well by inflow of dirty well fluid on the other hand. The two phases can be matched flexibly to the respective local circumstances. The heat released to the well fluid during the burnoff phase generally leads to heating of the well fluid above its boiling point and commencement of boiling thereof. In a preferred embodiment of the process according to the invention, the thermal opening of the inflow orifices is not initiated until the temperature of the outer wall of the device in the region of the at least one combustion chamber has cooled down to the boiling temperature of the well fluid in this region.

In a further preferred embodiment of the inventive device, the at least one inflow orifice with its closure element is within a middle region of the vessel. A stop element is arranged below the at least one inflow orifice on the outside of the vessel. A shell tube which is arranged around the vessel at the upper end of the vessel is secured by a thermally releasable securing element on the outer wall of the vessel. An upper combustion chamber present at the level of the securing element in the vessel comprises a further igniter and further fuel which, when it burns off, generates a temperature at which the securing element loses its integrity.

For performance of the process according to the invention, the inventive device is first introduced into the well and is preferably positioned such that the combustion chamber is at the level of the perforation region of the production zone. Subsequently, the fuel in the combustion chamber is ignited. Proceeding from the igniter, the fuel burns off in the combustion chamber. After the burnoff of the fuel in the combustion chamber, the closure element of the at least one inflow orifice is thermally opened, such that well fluid flows into the interior of the vessel. Since the at least one inflow orifice is in the middle region of the vessel, it is advantageous to close the inflow orifice prior to the withdrawal of the device from the well. This is done by igniting the further fuel in the upper combustion chamber. The burnoff of the further fuel heats the outer wall of the vessel in the region of the upper combustion chamber to such an extent that the securing element on the outer wall loses its integrity. The outer tube is released and slides downward owing to gravity along the outer wall of the vessel down to the stop element. The length of the shell tube is such that all inflow orifices are closed when the shell tube rests on the stop element. Since the upper combustion chamber is equipped with its own fuel and igniter, the inflow orifices can be closed independently in time from the burnoff operation and the inflow of the well fluid. After the closure of the inflow orifices, the well fluid is enclosed in the interior of the vessel and can be withdrawn from the well in the upward direction with the vessel.

The securing element which secures the shell tube on the outer wall of the vessel may be applied to the outer wall on the outside, for example as an adhesive bond or weld bond. In a further configuration, the securing element is at least one pushfit or screw connection between the shell tube and the wall of the vessel, which is manufactured from a material which, on exceedance of a given temperature limit, loses its integrity, for example a plastic. In a further configuration, a support ring is secured in or on the outer wall of the vessel, which holds the shell tube. In this case, the support ring is manufactured from a material which, on exceedance of a given temperature limit, loses its integrity, for example a plastic.

The stop element is fixed to the outer wall of the vessel, for example by screw connection, rivet connection or weld connection. It is configured such that it can absorb the forces which act on it on impact of the shell tube sliding downward, without damage to the stop element. The stop element is preferably manufactured from a steel. In a preferred configuration, the stop element is a component which extends radially outward in the form of a collar from the outer face of the vessel. The collar may consist of individual components or be configured as a surrounding component.

In a first variant of this embodiment, the combustion chamber and the hollow chamber are arranged from the bottom upward between the lower end of the vessel and the upper combustion chamber, the combustion chamber being separated from the hollow chamber by a separating element. In addition, the at least one inflow orifice is arranged at the upper end of the combustion chamber and the igniter at the lower end of the combustion chamber. The fuel is selected such that, after ignition, it burns off from the bottom upward and the burnoff of the fuel at the upper end of the combustion chamber generates a temperature at which both the at least one closure element and the separating element from the hollow chamber lose their integrity. In this variant, the inflow orifices are opened owing to the burnoff of the fuel in the combustion chamber as soon as the reaction front reaches the region of the inflow orifices.

In a second variant of this embodiment, the combustion chamber, a separation chamber, an orifice chamber and the hollow chamber are arranged from the bottom upward between the lower end of the vessel and the upper combustion chamber. The hollow chamber is bounded at the top and bottom by separating elements. The orifice chamber is arranged at the level of the at least one inflow orifice and has a further igniter and further fuel which, when it burns off, generates a temperature at which both the at least one closure element and the at least one separating element from the hollow chamber lose their integrity. In this variant, the burnoff of the fuel in the combustion chamber and the opening of the inflow orifices can be controlled independently in terms of time. This is enabled by the separation chamber comprising no fuel, thus ensuring thermal decoupling between fuel in the process of burnoff and the further fuel in the orifice chamber. The separation chamber can be separated by separating elements from the combustion chamber and the orifice chamber. The separation chamber may also be a region of the combustion chamber not filled with fuel.

In a third variant of this embodiment, the hollow chamber, the combustion chamber and a separation chamber are arranged from the bottom upward between the lower end of the vessel and the upper combustion chamber. The hollow chamber is separated from the combustion chamber by a separating element. The at least one inflow orifice is arranged at the lower end of the combustion chamber. The fuel in the combustion chamber is selected such that, when it burns off in the lower end of the combustion chamber, it generates a temperature at which both the at least one closure element and the separating element from the hollow chamber lose their integrity. As in the aforementioned variant, the separation chamber may be a separate chamber separated with separating elements, or be implemented as part of the combustion chamber unfilled with fuel. In this variant, the separation chamber fulfills the function of thermal decoupling of the combustion chamber and of the upper combustion chamber.

In a development of the invention, the thermal opening of the inflow orifices is brought about by an explosive charge. The explosive charge may be embedded within the fuel and may ignite owing to the evolution of heat. In a preferred embodiment, the explosive charge is used instead of the fuel and is ignited by a separate igniter. This configuration variant is advantageous especially in the case of embodiments with a separate orifice chamber. In configurations of the inventive apparatus with an explosive charge, the at least one inflow orifice and the closure device thereof are configured such that the closure element is forced out of the inflow orifice by the pressure and temperature rise after the explosion. In an advantageous configuration, the inflow orifice is configured so as to widen from the inside outward, more preferably in the form of a cone. Any separating elements present should be configured such that they lose their integrity after the explosion owing to the pressure and temperature rise.

The inventive device can be manufactured beforehand in individual parts and be transported to the well, for example individual pipe sections which are filled with fuel or which form hollow chambers. On site, the individual parts can simply be assembled and matched to the specific demands, for example by screwing together an appropriate number of pipe sections as required. Lengths of individual pipe sections from one to three meters are preferable from a manufacturing point of view and with regard to simple transport to the well. The total length of the device depends on the respective demands and may, for example, be from two to about fifty meters. The device can be introduced into the well and withdrawn again therefrom by known means such as a hoist and logging cables.

As well as the preferred embodiments mentioned, the invention also encompasses further configurations, for example combinations or modifications of the embodiments described.

The inventive device is notable for a simple construction, which is inexpensive to produce and easy to employ. A majority of the components can be reused repeatedly. The device can be manufactured in advance, optionally in individual parts, and be stored over a prolonged period without any problem. Especially in the case of use of an aluminothermic mixture as a fuel, no potentially harmful gases escape in the course of burnoff of the fuel.

In the course of performance of the process according to the invention, the well fluid which surrounds the device in the region of the combustion chamber in the process of burnoff is strongly heated. The well fluid begins to boil and at least partly vaporizes. The hot liquid and the vapor which forms penetrate into the perforation channels and generate turbulences and pressure pulses in the rock. This leaches encrustations and/or high-viscosity deposits out of the rock and thus cleans the perforation channel. This effect is enhanced as soon as the inflow orifices are opened and the pressure in the region close to the inflow orifices falls drastically. The soil detached is discharged from the perforation orifices into the well fluid, absorbed into the interior of the inventive device and transported from the well to the surface.

The process according to the invention brings about controlled and efficient stimulation and cleaning of the perforation region of the production zone. As a result, the fluids to be produced, such as mineral oil or natural gas, can again flow and be produced more easily through the perforation channels into the well.

The drawings hereinafter further illustrate the invention, though the drawings should be understood as schematic diagrams. They do not constitute any restriction of the invention, for example with respect to specific dimensions or configuration variants of components. For the sake of better illustration, they are generally not to scale, particularly with respect to length and width ratios. The figures show:

FIG. 1: embodiment of an inventive device with an inflow orifice at the lower end of the vessel

FIG. 2: embodiment of an inventive device with an inflow orifice at the upper end of the vessel

FIG. 3: embodiment of an inventive device with an inflow orifice in the middle region of the vessel

FIG. 4: variant of the embodiment with an inflow orifice in the middle region of the vessel

FIG. 5: variant of the embodiment with an inflow orifice in the middle region of the vessel

LIST OF REFERENCE NUMERALS USED

-   -   10 . . . well     -   11 . . . lining     -   12 . . . perforation orifices     -   13 . . . perforation channels     -   14 . . . production zone     -   15 . . . well bottom     -   16 . . . well fluid     -   20 . . . logging cable     -   21 . . . tubular vessel     -   22 . . . pipe segment     -   23 . . . segment connector     -   24 . . . separating element     -   25 . . . hollow chamber     -   26 . . . separation chamber     -   30 . . . combustion chamber     -   31 . . . fuel     -   32 . . . igniter     -   33 . . . reaction front     -   34 . . . residue     -   40 . . . orifice chamber     -   41 . . . inflow orifice     -   42 . . . closure device     -   43 . . . closure element     -   44 . . . plug     -   45 . . . securing device     -   46 . . . weight element     -   47 . . . connecting element     -   48 . . . further fuel     -   49 . . . further igniter     -   50 . . . upper combustion chamber     -   51 . . . further fuel     -   52 . . . further igniter     -   53 . . . shell tube     -   54 . . . securing element     -   55 . . . stop element

FIGS. 1 to 5 show schematic section drawings of a well in an underground deposit. The well 10 is provided with a lining 11, for example a steel pipe. The lining 11 prevents loose rock adjoining the well from falling into the well and formation fluids which are typically under pressure, such as formation water, from breaking through into the well in large volumes. The lining 11 has several perforation orifices 12. Known processes such as ball perforation or jet perforation produced perforation channels 13 in the production zone 14. Through the perforation channels 13, fluids to be produced, for example natural gas or mineral oil, flow through the perforation orifices 12 into the well 10 and can be produced to the surface.

The inner wall of the lining 11 has a cylindrical or stepwise cylindrical configuration with a circular cross section. In the case of a stepwise cylindrical configuration, the diameter of the circular cross section decreases stepwise in the axial downward direction. The tubular vessel 21 is connected via a suspension system to the logging cable 20, which can be moved by means of a hoist at the surface. The latter is not shown in the figures; corresponding devices are known to those skilled in the art. The hoist can be used to move the vessel 21 in the well 10 in axial direction. The outer diameter of the vessel 21 is preferably 10% to 30% less than the internal diameter of the lining 11 in the region of the production zone 14.

FIGS. 1 a to 1 d show a first preferred embodiment of an inventive device for cleaning a liquid-filled well. A tubular vessel 21 is secured by means of a suspension system to a logging cable 20. The vessel 21 is configured as a multipart pipe, of which the figure shows two pipe segments 22. The pipe segments 22 are connected to one another via segment connectors 23, for example by flange connections or screw connections. The pipe segments 22 can be produced from steel pipes as typically used in mineral oil production and referred to as “tubing”, for example of the H-40, C-75, N-80 or P-105 type.

From the inner face of the lower end, a combustion chamber 30 extends in the upward direction, this being filled by a fuel 31 and being concluded at the top by a separating element 24. The fuel is preferably an aluminothermic mixture which comprises the components Al, FeO, Fe₂O₃, Fe₃O₄ and/or SiO₂ and is present as a bed or pressed blocks in the combustion chamber. Particular preference is given to a thermite bed or pressed thermite blocks. The amount of the fuel 31 may be from a few kilograms up to several hundred kilograms and is fixed according to how great the amount of heat to be introduced into the well fluid is to be. The separating element 24 extends over the entire pipe cross section and is manufactured from a material which loses its integrity when the fuel burns off. Suitable materials are, for example, plastics, aluminum or an iron alloy with low melting point. The separating element concludes the combustion chamber 30 and thus protects the fuel, for example, from moisture. The space above the separating element 24 up to the upper end of the vessel is not filled with fuel and forms a hollow chamber 25. At the upper end of the combustion chamber 30, an igniter 32 which has been arranged within the fuel is suitable for igniting the fuel 31, for example an electric igniter such as a light arc igniter or spiral igniter, or a chemical igniter. The activation or ignition temperature depends on the composition of the fuel and may, in the case of an aluminothermic mixture, for example, be from 600° C. to 1300° C. The igniter can be ignited using a wire which is conducted from the igniter through the logging cable 20 up to the surface.

At the lower end of the tubular vessel 21 is arranged an inflow orifice 41 with its closure device 42. FIG. 1 b shows a more detailed view of the lower end of the vessel. In the example shown, the inflow orifice 41 is configured as a cone narrowing from the inside outward. The closure device 42 comprises a plug 44 which has a shape matched to the inflow orifice and which has been provided with a securing device 45 which limits the axial movement thereof away from the inflow orifice. The securing device 45 comprises a weight element 46 which is outside the tubular vessel 21 and is fixed to the plug via a steel rope as the flexible connecting element 47. The weight element in this example consists of a frustoconical base body on which three rods are mounted in homogeneous distribution over the circumference, protruding radially outward. The length of the rods is such that the diameter of the circle surrounding the rod ends is greater than the external diameter of the inflow orifice 41.

The weight element 46 can also be configured in other ways, for example with a spherical or disk-shaped base body with or without lateral projections. The base body may also consist of rods fixed to one another in a preferably crossed manner. The weight element is preferably manufactured from a metal, especially iron or steel, and has a mass of 20 to 40 kg. The flexible connecting element 47, especially a steel rope, preferably has a length of 0.5 m to 2 m.

The plug 44 is connected in a thermally releasable manner to the inside of the end by a closure element 43. The closure element 43 preferably takes the form of a weld seam or adhesive bond. With regard to integrity, the closure element 43 is preferably designed such that the connection between the inside of the end and the plug 44 at least withstands the hydrostatic pressure of the well fluid surrounding the vessel, provided that the fuel in the combustion chamber is not ignited. In this case, the weight that the fuel mass exerts on the plug 44 may be taken into account. The plug 44 itself is manufactured from a material which withstands the temperatures which exist in the course of burnoff of the fuel.

For performance of the process according to the invention, the tubular vessel 21 is first introduced into the well. If the cleaning of the well bottom 15 is the main aim, the vessel is positioned such that the lower end thereof is from 0.5 m to 5 m above the well bottom. The connecting element 47 in this case is preferably such that the weight element 46 after the positioning of the vessel rests on the well bottom. If, in contrast, the cleaning of the perforation region of the production zone 14 is the main aim, the vessel 21 is positioned such that the combustion chamber 30 is at the level of the perforation region of the production zone 14. In the example shown, both demands are present in combination; the well bottom 15 is just below the production zone 14. The weight element 46 of the securing device 45 rests on the well bottom 15.

After the positioning of the vessel 21, the fuel 31 in the combustion chamber 30 is ignited. Proceeding from the igniter 32, the fuel burns off in the combustion chamber, forming a reaction front 33 which passes downward through the combustion chamber in the course of burnoff. During the burnoff of the fuel in the upper region of the combustion chamber 30, temperatures are attained which lead to the separating element 24 losing its integrity, more particularly being thermally destroyed. Due to the evolution of heat, the well fluid which surrounds the device in the region of the combustion chamber 30 in the process of burnoff is strongly heated, such that it at least partly begins to boil. The hot liquid and the vapor which forms penetrate through the perforation orifices 12 into the perforation channels 13 and generate pressure pulses in the rock. This leaches encrustations and/or high-viscosity deposits out of the rock and thus cleans the perforation channels. As a result, the fluids to be produced, such as mineral oil or natural gas, can again flow more easily through the perforation channels into the well. The turbulences excited transport the soiling detached from the perforation channels into the well, and they are present in the well fluid.

As soon as the reaction front 33 reaches the lower region of the combustion chamber 30 in which the closure element 43 is present, this too loses its integrity owing to the temperature increase in the environment thereof. The plug 44 is released from the inflow orifice 41 and opens it, such that well fluid can flow into the hollow chamber. This state is shown in FIG. 1 c. The plug 44 is forced upward by the flow. The axial motion thereof away from the inflow orifice, however, is limited by the connecting element 47. The residue 34 resulting from the burnoff of the fuel is entrained with the flow and is distributed in the interior of the vessel 21. For absorption of well fluid, the entire volume of the combustion chamber 30 and of the hollow chamber 25 is available, minus the volume taken up by the residue 34. With the well fluid, particles released from the perforation channels, and also sand and sludge from the well bottom, are transported into the interior of the vessel. Depending on the dimensions of the vessel and the pressure difference between the inside of the vessel and the well fluid, the inflow operation may take from one to about ten minutes.

In one variant of the invention, the total length of the vessel 21 is selected such that the uppermost segment projects above the liquid level of the well fluid. In the liquid-free portion of the vessel, an orifice is provided, through which the interior of the vessel is connected to the ambient air, such that atmospheric pressure exists within the vessel. During the inflow operation, the air present within the vessel can escape, as a result of which the inflow time is shortened.

In a further variant, the inventive vessel 21 takes the form of a tubing string. This variant is used advantageously when the liquid column in the well is more than 100 meters in height. In this case, it is additionally advantageous, just above the perforation zone of the production zone 14, to use a packing around the vessel 21, this extending in the radial direction from the outer vessel wall up to the inner well wall. This restricts the region of the well fluid stimulated by the burnoff of the fuel in the combustion chamber, which leads to more intense stimulation of the perforation channels.

In one variant of this embodiment for cleaning of the well bottom, the mass of the weight element 46 is such that the weight is greater than the flow forces, such that the weight element remains lying on the well bottom during the inflow operation. In an alternative variant, the total mass of plug 44, connecting element 47 and weight element 46 is selected such that, after the thermal release of the closure element 43, the plug and the weight element secured thereto by the connecting element are pulled in the direction of the inside of the vessel 21 by the pressure of the adjoining well fluid. Since the radial extent of the weight element 46 in at least one spatial direction is greater than the diameter of the inflow orifice 41 on the outside of the lower end of the vessel, the weight element cannot get into the vessel. As a result, the axial movement of the plug away from the inflow orifice is limited. In this case, the weight element 46 is configured such that it does not completely block the inflow orifice 41, but allows the well fluid to flow around the weight element adjoining the inflow orifice into the vessel.

On conclusion of the inflow operation, the vessel 21 is withdrawn from the well in the upward direction. Under the action of gravity, the plug 44 falls back into the inflow orifice 41 under its own weight and closes it. This effect is enhanced by the weight of the weight element 46 which, during the withdrawal of the vessel 21, pulls downward on the plug. This situation is shown schematically in FIG. 1 d. The well fluid which has flowed into the vessel 21, with the soil particles and/or sand and sludge present therein, is enclosed therein and can be conveyed to the surface. This operation can be repeated several times if required. In this way, the perforation channels 13 and the well bottom 15 are effectively cleaned.

FIGS. 2 a and 2 b show a second preferred embodiment of an inventive device for cleaning a liquid-filled well. A tubular vessel 21 configured as a multipart pipe is secured on a logging cable 20 by means of a suspension system, the figures showing two pipe segments 22 thereof. The pipe segments 22 are connected to one another via segment connectors, for example by flange connections or screw connections. The two ends of the vessel 21 are closed and are manufactured from a material which withstands the temperatures which arise in the course of burnoff of the fuel.

A combustion chamber 30 which is filled with a fuel 31 and is completed in the upward direction by a separating element 24 extends upward from the inner face of the lower end. Preference is given to using the same fuels as described above for FIG. 1. The separating element 24 extends over the entire tube cross section and is manufactured from a material which loses its integrity when the fuel burns off. The separating element concludes the combustion chamber 30 and thus protects the fuel, for example, from moisture. At the upper end of the combustion chamber 30, an igniter 32 is arranged in the fuel, this being suitable for igniting the fuel, for example an electrical igniter such as a light arc igniter or spiral igniter, or a chemical igniter. The igniter can be ignited by means of a wire which is conducted from the igniter through the logging cable 20 up to the surface. The length of the combustion chamber preferably corresponds to the axial dimension of the perforation region of the production zone 14 and may be several meters.

The space above the separating element 24 is not filled with fuel and forms a hollow chamber 25. The length thereof may be much longer than the length of the combustion chamber and may, for example, be from a few meters up to approx. 50 meters. The hollow chamber 25 is closed at the top by a further separating element 24. The space above the further separating element up to the upper end of the vessel 21 is provided with further fuel 48, especially a thermite mixture, and a further igniter 49, and forms the orifice chamber 40. The length thereof may be up to about one meter. In the outer wall of the vessel 21, in the region of the orifice chamber 40, several inflow orifices 41 are arranged with their closure devices 42. In the example shown, the inflow orifices 41 are arranged in two rows one on top of the other, distributed homogeneously over the circumference of the vessel. Each inflow orifice 41 is configured as a cone narrowing from the inside outward. The closure devices 42 in this example each comprise only one connecting element whose shape is matched to the inflow orifice in the form of a plug and which is manufactured from a material which loses its integrity when the further fuel 48 is burnt off. The closure devices may also be configured analogously to the embodiment according to FIG. 1 as a plug with an additional closure element which is connected in a thermally releasable manner to the inside of the wall of the orifice chamber and the plug.

To perform the process according to the invention, the tubular vessel 21 is first introduced into the well and positioned such that the combustion chamber 30 is at the level of the perforation region of the production zone 14. Subsequently, the fuel 31 in the combustion chamber 30 is ignited. Proceeding from the igniter 32, the fuel in the combustion chamber burns off, forming a reaction front which passes downward through the combustion chamber in the course of burnoff. During the burnoff of the fuel in the upper region of the combustion chamber 30, temperatures are attained which lead to thermal destruction of the separating element 24 between the combustion chamber and the hollow chamber 25. Depending on the case, the amount of fuel may be from 10 kg to 300 kg. In the case of use of a thermite mixture as the fuel, this reacts within a few minutes to form liquid metal and a slag as a residue. The heat stored in the metal and the slag is released to the well fluid over a period of one to about five hours. Owing to this evolution of heat, the well fluid which surrounds the device in the region of the combustion chamber 30 in the process of burnoff is strongly heated, such that it at least partly begins to boil. The hot liquid and the vapor which forms penetrate through the perforation orifices 12 into the perforation channels 13 and clean them.

On conclusion of the burnoff in the combustion chamber 30, the further fuel 48 is ignited with the aid of the further igniter 49 in the orifice chamber 40. In a preferred variant, this ignition is delayed until the outside temperature of the vessel has again gone below the boiling temperature of the well fluid. The burnoff generates a temperature at which both the closure elements and the separating element 24 from the hollow chamber 25 lose their integrity. The inflow orifices 41 are opened as a result, and well fluid with the soil and/or sand particles present therein flows into the interior of the vessel 21. As well as the volume of the hollow chamber 25, the volume of the combustion chamber 30 not filled with residues 34 from the burnoff is also available for accommodation of well fluid. FIG. 2 b shows the inventive device after conclusion of the inflow operation. In this embodiment, the closure of the inflow orifices 41 after the inflow of the well fluid is not required, since the inflow orifices are at the upper end of the vessel 21. The well fluid is enclosed in the interior of the vessel and can be withdrawn from the well with the vessel in the upward direction.

By raising or lowering the vessel 21 in the well prior to the opening of the inflow orifices or during the inflow phase, it is possible in a controlled manner to influence the region of the production zone 14 from which the well fluid is drawn off. The process according to the invention enables controlled and efficient stimulation and cleaning of the perforation region of a well.

FIGS. 3 a to 3 c show a third preferred embodiment of an inventive device for cleaning a liquid-filled well. A tubular vessel 21 configured as a multipart pipe is secured on a logging cable 20 by means of a suspension system, the figure showing two pipe segments 22 thereof. The pipe segments 22 are connected to one another via segment connectors, for example by flange connections or screw connections. Both ends of the vessel 21 are closed and are manufactured from a material which withstands the temperatures which arise in the course of burnoff of the fuel.

A combustion chamber 30 which is filled with a fuel 31 and is concluded at the top by a separating element 24 extends upward from the inner face of the lower end of the vessel 21. The separating element 24 extends over the entire pipe cross section and is manufactured from a material which loses its integrity when the fuel is burnt off. The separating element 24 concludes the combustion chamber 30 and thus protects the fuel, for example, from moisture. Below the separating element, at the upper end of the combustion chamber 30, there are several inflow orifices 41 with their closure devices 42. With regard to the axial extent of the vessel 21, the inflow orifices 41 are in the middle region of the vessel 21.

In the example shown, the inflow orifices 41 are arranged in two rows one on top of another, distributed homogeneously over the circumference of the vessel 21. Each inflow orifice 41 is configured as a cone narrowing from the inside outward. The closure devices 42 in this example each comprise just one closure element whose shape is matched to the inflow orifice in the form of a plug and which is manufactured from a material which loses its integrity when the fuel 31 in this region is burnt off. The closure devices 42 may also be configured analogously to the embodiment according to FIG. 1 as a plug with an additional closure element which is connected in a thermally releasable manner to the inside of the wall of the vessel and the plug.

At the lower end of the combustion chamber 30, an igniter 32 is arranged in the fuel, this being suitable for igniting the fuel, for example an electrical igniter such as a light arc igniter or spiral igniter, or a chemical igniter. The igniter can be ignited via a wire which is conducted from the igniter through the logging cable 20 up to the surface. The length of the combustion chamber preferably corresponds to the axial extent of the perforation region of the production zone 14 and may be several meters. The fuel 31 is selected such that, after ignition, it burns off from the bottom upward and, when it burns off at the upper end of the combustion chamber, generates a temperature at which both the closure elements of the closure devices 42 and the separating element 24 lose their integrity.

The space above the separating element 24 is not filled with fuel and forms a hollow chamber 25. The hollow chamber is closed in the upward direction by a further separating element 24. The space above the further separating element up to the upper end of the vessel 21 is provided with further fuel 51, especially a thermite mixture, and a further igniter 52, and forms the upper combustion chamber 50. The axial extent of the upper combustion chamber is preferably from 0.5 m to 1 m.

At the upper end of the vessel 21, a shell tube 53 is arranged around the vessel, this being secured on the outer wall of the vessel with a thermally releasable securing element 54. Within the vessel, the upper combustion chamber 50 is at the level of the securing element 54. The fuel 51 in the upper combustion chamber 50, when it burns off, generates a temperature at which the securing element loses its integrity. In the example described, the securing element 54 is a number of point weld connections which hold the shell tube 53 in its axial position at the upper end of the vessel 21. The weld points are designed so as to melt at the temperatures which prevail when the fuel 51 in the upper combustion chamber 50 is burnt off.

Below the inflow orifices 41, a stop element 55 is arranged on the outside of the vessel 21 and is fixed thereto. The stop element 55 in this example is designed as a surrounding steel collar welded to the outer wall of the vessel.

To perform the process according to the invention, the tubular vessel 21 is first introduced into the well and positioned such that the combustion chamber 30 is at the level of the perforation region of the production zone 14. Subsequently, the fuel 31 in the combustion chamber 30 is ignited. Proceeding from the igniter 32, the fuel in the combustion chamber burns off, forming a reaction front which passes from the bottom upward through the combustion chamber in the course of burnoff. During the burnoff of the fuel in the upper region of the combustion chamber 30, temperatures are attained which lead to thermal destruction of the separating element 24 between the combustion chamber and the hollow chamber 25. Depending on the case, the amount of fuel may be from 10 kg to 300 kg. In the case of use of a thermite mixture as the fuel, this reacts within a few minutes to form liquid metal and a slag as a residue. Owing to the evolution of heat by the burnoff, the well fluid which surrounds the device in the region of the combustion chamber 30 in the process of burnoff is strongly heated, such that it at least partly begins to boil. The hot liquid and the vapor which forms penetrate through the perforation orifices 12 into the perforation channels 13 and clean them.

As soon as the reaction front reaches the upper end of the combustion chamber 30, the closure elements of the closure devices 42 are thermally opened. The inflow orifices 41 are opened as a result, and well fluid with the soil and/or sand particles present therein flows into the vessel 21. As well as the volume of the hollow chamber 25, the volume of the combustion chamber 30 not filled with residues 34 from the burnoff is also available for accommodation of well fluid. FIG. 3 b shows the inventive device after conclusion of the inflow operation.

Since inflow orifices 41 are present in the middle region of the vessel 21, it is advantageous to close the inflow orifices prior to the withdrawal of the device from the well. This is done by igniting the further fuel 51 in the upper combustion chamber 50. The burnoff of the further fuel 51 heats the outer wall of the vessel in the region of the upper combustion chamber to such an extent that the securing element 54 on the outer wall loses its integrity. The shell tube 53 is released and it slides downward owing to gravity along the outer wall of the vessel down to the stop element 55. This state is shown in FIG. 3 c. The length of the shell tube 53 is such that all inflow orifices 41 are closed when the shell tube rests on the stop element. The length of the shell tube is preferably 1.5 times to twice the axial extent of the inflow orifices on the outside of the vessel, for example two meters in the case of an extent of the inflow orifices of one meter.

Since the upper combustion chamber 50 is equipped with its own fuel 51 and igniter 52, the inflow orifices can be closed independently in terms of time from the burnoff operation and the inflow of the well fluid. After the closure of the inflow orifices, the well fluid is enclosed within the vessel and can be withdrawn from the well in the upward direction with the vessel. By raising or lowering the vessel 21 in the well prior to the opening of the inflow orifices or during the inflow phase, it is possible to influence in a controlled manner the region of the production zone 14 from which the well fluid is drawn off. The process according to the invention enables controlled and efficient stimulation and cleaning of the perforation region of a well.

FIG. 4 shows a variant of the third preferred embodiment, in which are arranged, between the lower end of the vessel 21 and the upper combustion chamber 50, from the bottom upward, the combustion chamber 30, a separation chamber 26, an orifice chamber 40 and the hollow chamber 25. The hollow chamber 25 is bounded at the top and bottom by separating elements 24. The orifice chamber 40 is arranged at the level of the inflow orifices 41 and has a further igniter 49 and a further fuel 48. The separation chamber 26 in this example is separated by separating elements from the combustion chamber 30 and the orifice chamber 40. It can also be implemented in other ways, for example by virtue of an upper section of the combustion chamber not being filled with fuel.

Below the lower inflow orifices 41, a stop element 55 is mounted on the outside of the vessel 21. At the upper end of the vessel 21, at the level of the upper combustion chamber 50, a shell tube 53 is arranged around the vessel, which is secured on the outer wall of the vessel with a thermally releasable securing element 54.

The process is performed in a similar manner to that described by FIGS. 3 a to 3 c. The difference is that, in the embodiment according to FIG. 4, the phases of the fuel burnoff in the combustion chamber 30 and the phase of inflow of well fluid into the vessel 21 are controllable independently in terms of time. First of all, with the aid of the igniter 32, the burnoff of the fuel 31 in the combustion chamber is started. This thermally destroys the separating element from the separation chamber 26. The dimensions of the separation chamber are such that the heat which arises in the course of burnoff of the fuel 31 is insufficient to also destroy the separating element from the orifice chamber 40 or to ignite the further fuel 48 in the orifice chamber.

Only after conclusion of the burnoff in the combustion chamber 30 is the further fuel 48 in the orifice chamber 40 ignited with the aid of the further igniter 49. In a preferred variant, this ignition is delayed until the outside temperature of the vessel again goes below the boiling temperature of the well fluid. The burnoff generates a temperature at which both the closure elements of the closure devices 42 and the separating elements from the hollow chamber 25 and from the separation chamber 26 lose their integrity. The inflow orifices 41 are opened as a result, and well fluid with the soil and/or sand particles present therein flows into the vessel 21.

As well as the volume of the hollow chamber 25, the volume of the combustion chamber 30, of the separation chamber 26 and of the orifice chamber 40 not filled with residues 34 from the burnoff is available for accommodation of well fluid. The closure of the inflow orifices 41 and the withdrawal of the device from the well are effected as described for FIGS. 3 a to 3 b.

FIG. 5 shows a further variant of the third preferred embodiment, in which are arranged, between the lower end of the vessel 21 and the upper combustion chamber 50, from the bottom upward, the hollow chamber 25, the combustion chamber 30 and a separation chamber 26. The hollow chamber 25 is separated from the combustion chamber 30 by a separating element 24. At the lower end of the combustion chamber are arranged inflow orifices 41 with their closure devices 42. Below the lower inflow orifices 41 is mounted a stop element 55 on the outside of the vessel 21. At the upper end of the vessel 21, at the level of the upper combustion chamber 50, a shell tube 53 is arranged around the vessel, this being secured by a thermally releasable securing element 54 on the outer wall of the vessel.

The performance of the process according to the invention corresponds essentially to that described by FIGS. 3 a to 3 c. The difference is that the burnoff of the fuel 31 in the combustion chamber 30 in the present example proceeds from the top downward.

In all embodiments with a shell tube 53 which is provided for closure of the inflow orifices 41, it has to be ensured that the shell tube can slide unhindered from its starting position down to the stop element 55. If the tubular vessel 21 is composed of several pipe segments, the segment connectors 23 therefore have to be selected accordingly, for example as screw connections. 

1. A device for cleaning a liquid-filled well, comprising a tubular vessel, the interior of which comprises at least one combustion chamber and at least one hollow chamber arranged in longitudinal succession, the combustion chamber being at least partly filled with a fuel and having an igniter, and the tubular vessel having at least one inflow orifice through which well fluid can flow from the outside into the tubular vessel, wherein the at least one inflow orifice is provided with a closure device comprising at least one closure element which loses its integrity on exceedance of a given temperature, such that the closure device opens.
 2. The device according to claim 1, wherein the combustion chamber is at a lower end of the tubular vessel, and the at least one inflow orifice with its closure device is arranged at the lower end of the tubular vessel.
 3. The device according to claim 2, wherein: the inflow orifice is configured so as to narrow from the inside outward; the closure device comprises a plug whose shape has been matched to the inflow orifice; the plug is provided with a securing device which restricts the axial movement thereof away from the inflow orifice; and the plug is connected in a thermally releasable manner to the inside of the end by virtue of the closure element.
 4. The device according to claim 3, wherein: the securing device comprises a connecting element and a weight element which is outside the vessel; the connecting element is connected to the weight element and the plug; and a radial extent of the weight element at least in one spatial direction is greater than the diameter of the inflow orifice on the outside of the lower end of the tubular vessel.
 5. The device according to claim 1, wherein: the combustion chamber is at the lower end of the tubular vessel; the hollow chamber is arranged above the combustion chamber; above the hollow chamber in turn is arranged an orifice chamber which is separated therefrom by a separating element and in the wall of which there is at least one inflow orifice with its closure device; and a further igniter and further fuel are present in the orifice chamber, said further fuel, when it burns off, generating a temperature at which both the at least one closure element and the separating element from the hollow chamber lose their integrity.
 6. The device according to claim 1, wherein: the at least one inflow orifice with its closure element is within a middle region of the vessel; a stop element is arranged below the at least one inflow orifice on the outside of the vessel; a shell tube which is arranged around the vessel at the upper end of the vessel is secured by a thermally releasable securing element on the outer wall of the vessel; and an upper combustion chamber present at the level of the securing element in the vessel comprises a further igniter and further fuel which, when it burns off, generates a temperature at which the securing element loses its integrity.
 7. The device according to claim 6, wherein the combustion chamber and the hollow chamber are arranged from the bottom upward between the lower end of the vessel and the upper combustion chamber, the combustion chamber being separated from the hollow chamber by a separating element, and the at least one inflow orifice being arranged at the upper end of the combustion chamber and the igniter at the lower end of the combustion chamber, and the fuel being selected such that, after ignition, it burns off from the bottom upward and the burnoff of the fuel at the upper end of the combustion chamber generates a temperature at which both the at least one closure element and the separating element from the hollow chamber lose their integrity.
 8. The device according to claim 6, wherein: a separation chamber, an orifice chamber and the combustion chamber are arranged from the bottom upward between the lower end of the vessel and the upper combustion chamber; the hollow chamber is bounded at the top and bottom by separating elements; and the orifice chamber is arranged at the level of the at least one inflow orifice and has a further igniter and further fuel which, when it burns off, generates a temperature at which both the at least one closure element and the separating element from the hollow chamber lose their integrity.
 9. The device according to claim 6, wherein: the hollow chamber, the combustion chamber and a separation chamber are arranged from the bottom upward between the lower end of the vessel and the upper combustion chamber; the hollow chamber is separated from the combustion chamber by a separating element; the at least one inflow orifice is arranged at the lower end of the combustion chamber; and the fuel in the combustion chamber is selected such that, when it burns off in the lower end of the combustion chamber, it generates a temperature at which both the at least one closure element and the separating element from the hollow chamber lose their integrity.
 10. The device according to claim 1, wherein the fuel in the combustion chamber is a metallothermic mixture.
 11. A process for stimulating and cleaning a liquid-filled well, the process comprising: (a) introducing a device according to claim 1 into a liquid-filled well; (b) igniting the fuel in the at least one combustion chamber; (c) thermally opening the closure element of the at least one inflow orifice, such that well fluid can flow into the at least one hollow chamber; (d) optionally closing the at least one inflow orifice; and (e) withdrawing the device from the well.
 12. The process according to claim 11, wherein, in step (a), the device is positioned in the well such that the combustion chamber is at the level of a perforation region of the production zone.
 13. The process according to claim 11, wherein step (c) is preceded by positioning of the device in the well such that the at least one inflow orifice is at the level of a perforation region of the production zone.
 14. The process according to claim 11, wherein step (c) is not initiated until a temperature of the outer wall of the device in the region of the at least one combustion chamber has cooled to a boiling temperature of the well fluid in this region. 